Fluid injection head structure and method for manufacturing the same

ABSTRACT

The present invention provides a fluid injection head structure and a method of fabricating the same. The fluid injection head structure is disposed on a substrate and has a bubble generator, a functional device for control the bubble generator, a first conductive trace composed of poly-silicon, a chamber, a manifold in flow communication with the chamber, and a second conductive trace. The second conductive trace electrically couples the functional device with the bubble generator and the first conductive trace. Moreover, the chamber further has at least one orifice through the substrate and a gate and the first conductive trace are formed in the same photo-etching process (PEP).

BACKGROUND OF INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a fluid injection headstructure, and more particularly, to a fluid injection head structurewith conductive traces made of one single metal layer and one singlepoly-silicon layer.

[0003] 2. Description of the Related Art

[0004] Fluid injection devices are widely applied in ink jet printers.As a reliability of ink jets have improved, the cost of manufacturingink jets has reduced significantly. Ink jets offering high-qualitydroplets with a high frequency and a high spatial resolution arecommonplace. Fluid injection devices can be applied to many other fieldsin advance, such as fuel injection systems, cell sorting, drug deliverysystems, print lithography, and micro jet propulsion systems.

[0005] Among all available products, some use a method of center feedingfor ink supply, such as the model of C6578 cartridge of theHewlett-Packard Company, and some use a method of edge feeding, such asthe model of HP51645 cartridge of the Hewlett-Packard Company. In theformer method, a sand blasting, laser drilling, or chemical etchingprocess is performed to create a manifold through the center of thechips for feeding ink. However, this method requires a large chip size,and the area above the manifold is wasted, leading to needlessly highmanufacturing costs. Although the process of penetrating through chipsis not needed in the latter method, two metal layers and a poly-siliconlayer are still needed. Therefore, many photo masks are used, and boththe time and cost of fabrication are increased.

[0006] U.S. Pat. No. 5,774,148, “Print head with field oxide as thermalbarrier in chip”, mentions a method for transmitting signals. A secondmetal layer is electrically connected to a first metal layer through avia and signals are transmitted between a heater 44 and a MOSFET device.Additionally, a poly-silicon layer is used as a gate of MOSFET deviceand a contact layer is used to electrically connect to the first metallayer for transmitting signals.

SUMMARY OF INVENTION

[0007] It is therefore a primary objective of the present invention toprovide a fluid injection head structure and a method of manufacturingthe same with conductive traces made of one metal layer and onepoly-silicon layer to simplify the manufacturing process and lowermanufacturing costs.

[0008] In a preferred embodiment, the fluid injection head structurecomprises a substrate, a bubble generator, a functional device tocontrol the bubble generator, a first conductive trace made of apoly-silicon layer, a chamber, a manifold connected to the chamber suchthat fluid can flow through the manifold to the chamber, and a secondconductive trace to electrically connect to the functional device andthe bubble generator, and the functional device and the first conductivetrace. In addition, the chamber further comprises an orifice in a topsurface of the substrate. Moreover, a gate of the functional device andthe first conductive trace are formed in the same photo-etching process(PEP).

[0009] It is an advantage of the present invention that only one metallayer and one polysilicon layer are used as conductive layers of thefluid injection head structure. The present invention overcomes theproblem of time delay and heat generation. The fabrication method of thepresent invention also helps to reduce manufacturing expenses andfabrication time.

[0010] These and other objectives of the present invention will notdoubt become obvious to those of ordinary skill in the art after readingthe following detailed description of the preferred embodiment, which isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0011]FIG. 1 is a cross-sectional diagram of a print head structureaccording to the present invention.

[0012]FIG. 2 is a cross-sectional diagram of a fluid injection headstructure of an embodiment according to the present invention.

[0013]FIG. 3 is a top view of the fluid injection head structure of thepresent invention.

[0014]FIG. 4 is a local amplified diagram of the fluid injection headchip shown in FIG. 3.

[0015]FIG. 5 is a schematic diagram of a matrix driving circuit in thefluid injection head of the present invention.

[0016]FIG. 5A is a schematic diagram of transmitting signals throughaddress lines.

[0017]FIG. 5B is an equivalent circuit of the fluid injection head atP1-A1.

[0018]FIG. 5C is an equivalent circuit of the fluid injection head atP16-A1.

[0019]FIG. 5D is a schematic diagram of HSPICE simulate of theequivalent circuits shown in FIG. 5B and FIG. 5C.

[0020]FIG. 6 to FIG. 8 are schematic diagrams of forming the fluidinjection head according to the present invention.

DETAILED DESCRIPTION

[0021] Please refer to FIG. 1, which is a cross-sectional diagram of aprint head structure according to the present invention. A fluidinjection head structure with a virtual valve is used in the presentinvention. As shown in FIG. 1, a bubble generator 14 comprises twobubble generating devices, a first heater 14 a and a second heater 14 b,disposed adjacent to an orifice 12. Because of differences, such asdifferent resistances, between the two heaters 14 a, 14 b, when the twoheaters 14 a, 14 b heat fluid (not shown) inside the chamber 16, twobubbles are generated in turn. A first bubble (not shown) is generatedby the first heater 14 a, closer to a manifold 11 than the second heater14 b, wherein the first bubble isolates the manifold 11 from an orifice12 and acts as a virtual valve to reduce a cross talk effect betweenthis chamber 16 and neighboring chambers 16. Then, a second bubble (notshown) is generated by the second heater 14 b. The second bubblesqueezes fluid, such as ink, inside the chamber 16 to eject out of theorifice 12. Finally, the second bubble combines with the first bubble soas to reduce the generation of satellite droplets.

[0022] The fluid injection head structure of the present invention feedsink successfully without fully etching through the chips. Based on thisstructure, power line layouts can be designed above the manifold 11. Notcounting the resistance layers, only one single poly-silicon layer andone single metal layer (SPSM) process is performed in the presentinvention.

[0023] Please refer to FIG. 2, which shows a cross-sectional diagram ofa fluid injection head structure according to the present invention. Alow temperature oxide layer 18 is, deposited on top of the bubblegenerator 14. After that, a via layer is formed in a predetermined areaand a metal layer 13 is deposited on the top surface of the heaters 14 aand 14 b through the via layer. Thus, the metal layer 13 is electricallyconnected to the heaters 14 a and 14 b.

[0024] In the same manner, a drain 68 and a source 66 of a MOSFET 15 areelectrically connected to the heaters 14 a and 14 b, and a ground 20 viathe metal layer 13. When a gate 64 of the MOSFET 15 is turned on, anexternal voltage signal is applied to the print head from a pad of themetal layer 13. A current flows from the pad via the metal layer 13 tothe first heater 14 a and the second heater 14 b. Then, the currentpasses through the drain 68 and the source 66 to the ground 20 so as tocomplete a heating process. As the ink inside the chamber 16 is heated,two bubbles are generated to squeeze ink droplets out of the orifice 12.It dependents upon the data to be printed to control which orifice 12ejects ink droplets during a printing process. The material of the metallayer 13 is any one of aluminum, gold, copper, tungsten, alloys ofaluminum-silicon-copper, or alloys of aluminum-copper.

[0025] Please refer to FIG. 3 and FIG. 4. FIG. 3 is a top view of theprint head according to the present invention. In the preferredembodiment, the orifice 12 of the print head is divided into sixteenPgroups, P1 to P16, and each Pgroup comprises twenty-two addresses A1 toA22. As shown in FIG. 5, which shows a schematic diagram of a matrixdriving circuit, a select signal is generated by a logic circuit or amicroprocessor 32 according to the data to be printed. Then, the selectsignal is transmitted to a power driver 34 and an address driver 35 todetermine which A (A1 to A22) should be turned on and to which P (P1 toP1 6) the power should be provided. For example, providing power to P1and turning on A22, the heaters 14 a and 14 b on the MOSFET 15 of P1 A22will complete an operation of heating and ejecting ink at thepredetermined time.

[0026]FIG. 4 is a local amplified diagram of the region B shown in FIG.3. Two rows of orifices 12 are positioned on the center of the chip.Dividing the orifices into two parts by a line A-A″ shown in FIG. 3,there are eight groups comprising P1 to P8 on the right and eight groupscomprising P9 to P16 on the left. The place above the manifold 11between the two rows of orifices 12 is used for a power line layout.Eight metal power lines corresponding to P1 to P8 are positioned to theright of the line A-A″ and electrically connected to I/O pads on theright. In the same manner, eight power lines corresponding to P9 to P16(not shown) are positioned on the left of the line A-A″ and electricallyconnected to I/O pads on the left.

[0027] The driving circuit between each corresponding P pad and G paduses a U-type circuit layout. The driving circuit between the pad P1 andthe pad G1 is illustrated in a dashed block in FIG. 4. Each drivingcircuit is connected without crossing any other driving circuit. Onlyone metal layer 13 is used to form the power line 19 between the heaters14 a, 14 b and the grounding pad G. There are eleven metal lines 22positioned above the groups of MOSFET 15 and another eleven metal lines22 positioned below the groups of MOSFET 15 in the page 4. The metallines 22 are electrically connected to the pads A so as to transmit theoutput data of the address driver 35 to the corresponding MOSFET 15 tocontrol ink ejection. There are also eleven poly-silicon lines 23positioned to the left of the groups of MOSFET 15 and another eleven tothe right of the groups of MOSFET 15. Then, contact layers 24 are formedto electrically connect the metal lines 22 and the poly-silicon lines 23to complete the connection of the driving circuits. The poly-siliconlines 23 are used to connect the metal lines 22 above and below thegroups of MOSFET 15 (i.e. the upper parts and lower parts of the metallines 22 in the FIG. 4). For example, if a signal is input from the padA1 to turn on the heaters of P16, it has to be transmitted via thepoly-silicon lines 23 through the metal lines 22 to the heaters of P16.

[0028] Please refer to FIG. 5A to FIG. 5D, which show schematic diagramsof circuits for transmitting signals with the silicon line 23 accordingto the present invention. Although a poly-silicon line 23 with a lengthof 2901 μm is used as an address conductive trace A1 to A22, theelectrical characteristics of the circuits are not deteriorated. First,very little current exists in the gate 64 of the MOSFET 15 so the heateffect of the poly-silicon lines 23 can be ignored. Second, as shown inFIG. 5A, resistance in the conductive trace is increased due to thepoly-silicon line 23 may occur the problem of time delay when theheaters in A1 of all P groups (including P1 to P16) inject. Take two A1addresses with the largest distance between them, A1-P1 and A1-P16, asexample. During printing operation, the frequency of ink-jet printing isset at about 10 KHz. Each address has a switching time of about 3.5 μs.Timing of a power supply for a P group must be within a pulse width of3.5 μs so that the timing for power supply of a P group is about 2 μs.This means that there is only a time buffer of about 500 ns between eachneighboring address. These limitations must be met or errors may occur.For example, in the group P1, the printhead A1 stops and the printheadA2 starts to inject, but the printhead A1 in the group P16 may still beinjecting.

[0029] Please refer to FIG. 5A. According to the sheet resistances ofthe metal line 22 (0.1 Ω/μm) and the poly-silicon line 23 (10 Ω/μm), theequivalent resistances of A1P1 and A1P16 while the gate 64 of all MOSFETdevice 15 is turned on can be obtained. The equivalent circuit of A1P1circuit is shown as FIG. 5B and that of A1P16 circuit is shown as FIG.5C. In contrast to A1P1, a signal must pass through additionalpolysilicon line 23 and a metal line 22 when transmitted to A1P16. Theresistance R1 of the additional poly-silicon line 23 is about 2901 Ω,and the resistance R2 of the additional metal line 22 is about 147 Ω. AHSPICE simulate is performed for these two circuits and a result isshown in FIG. 5D. Comparing time of the clock 50% of A1P1 and A1P16,which are 710 and 716 ns respectively, therefore, the time delay is onlyabout 8 ns. Comparing to the time delay endurance of 500 ns, the timedelay of the present invention has no influence on ink injecting.

[0030] Please refer to FIG. 6 to FIG. 8, which show schematic diagramsof forming the fluid injection head according to the present invention.First, a local oxidation process is performed to form a field oxidelayer 62 on a silicon substrate 60. A blanket boron implantation processis performed to adjust the threshold voltage of the driving circuit. Apoly-silicon gate 64 is formed in the field oxide layer 62. At the sametime, twenty-two poly-silicon lines 23 are formed on both edges of thechip. An arsenic implantation is performed to form a source 66 and adrain 68 on both sides of the gate 64. Then a low stress layer 72 suchas silicon nitride is deposited to form an upper layer of the chamber 16as shown in FIG. 6.

[0031] Please refer to FIG. 7. An etching solution (KOH) is used to etcha back side of substrate 60 to form a manifold 11 for fluid supply. Thenthe field oxide layer 62 is partially removed with an etching solution(HF) to form the chamber 16. After that, a precisely-timed etchingprocess using KOH is performed to increase the depth of the chamber 16.The chamber 16 and the manifold 11 are connected and filled with fluid,however this etching process needs special attention because convexcorners in the chamber 16 are also etched.

[0032] Next, a process of forming heaters is performed. This processshould be obvious to those of ordinary skill in the art. A good choiceof materials to use for the first heater 14 a and the second heater 14 bis alloys of tantalum and aluminum, but other materials like platinum orHfB₂ can also work effectively. A low temperature oxide layer 74 isdeposited over the entire substrate 60. In addition to protecting thefirst heater 14 a and the second heater 14 b and isolating the MOSFET15, the low temperature oxide layer 74 serves as a protective layer thatcovers the gate 64, the source 66, the drain 68, and the field oxide 62.

[0033] Next, a conductive layer 13 is formed on the first heater 14 aand the second heater 14 b to electrically connect the first heater 14a, the second heater 14 b, and the MOSFET 15 of the driving circuit. Thedriving circuit transmits a signal to individual heaters and drives aplurality of pairs of heaters, so that fewer circuit devices and linkingcircuits are required. The preferred material for the conductive layer13 is an alloy of aluminum-silicon-copper, aluminum, copper, gold, ortungsten. A low temperature oxide layer 76 is deposited as a protectionlayer on the conductive layer 13.

[0034] Please refer to FIG. 8. An orifice 12 is formed between the firstheater 14 a and the second heater 14 b. So far, the specification hasdetailed the formation of a fluid injector array with a driving circuitintegrated in one piece. The driving circuit and heaters are integratedon the same substrate and an integrated injection head structure isformed without the need for an attached nozzle plate.

[0035] The present invention uses a single poly-silicon and a singlemetal (SPSM) process to complete the circuit connection. Thepoly-silicon lines 23 and the gate 64 can be formed in a photo-etchingprocess (PEP) to simplify the manufacturing process. The presentinvention not only avoids using a second metal layer, but also completesthe function of the MOSFET 15 without affecting performance.

[0036] The following is a detailed description of the operation of thepresent invention. Please refer to FIG. 4 and FIG. 5. When printingstarts, the logic circuit or microprocessor 32 determines which orifices12 should eject ink according to the data to be printed and generates aselect signal. The select signal is transmitted to the power driver 34and the address driver 32 to turn on the proper A groups (A1 to A22) andapply power to the proper P groups (P1 to P1 6). Thus, a current isgenerated and applied to the heaters 14 a and 14 b to heat fluid andgenerate bubbles so that ink droplets are ejected. For example, supposethat a droplet is to be ejected from the orifice 12 a of A1P1. First, avoltage signal is input from an I/O pad of A1 and transmitted to thegate 64 of MOSFET 15 to turn on the gate 64. Next, another voltagesignal is input from an I/O pad of P1 to generate a current. The currentpasses via the heaters 14 a and 14 b to the drain 68, the source 66, andthe ground 20 so as to heat the fluid and generate bubbles. The bubblesact to eject an ink droplet from the orifice 12 a of A1P1.

[0037] Although the above description details a monochromatic printer,the present invention can be applied to color printers or multi-colorprinters. In addition, the present invention also can be applied toother fields, such as fuel injection systems, cell sorting, drugdelivery systems, print lithography, micro inject propulsion systems,and others.

[0038] According to the present invention, only a single poly-siliconprocess and a single metal process are used to complete circuit layoutsof the whole chip. There are several advantages of the presentinvention. The fluid injection head of the present invention uses twofewer photo masks than other similar products and therefore the cost ofthe photolithography processes are reduced. Moreover, fabricating timeis reduced and throughput is improved. Since ink is supplied without therequirement of etching through the entire chip, the circuit layouts canbe performed above the manifolds, leading to a reduction in wafer sizeand an increase the number of dies per wafer. Using this method ofimproving layout integration, the area required for circuit layout isreduced, and more orifices can be disposed in the same wafer area toimprove the printing speed.

[0039] Those skilled in the art will readily observe that numerousmodifications and alterations of the device may be made while retainingthe teachings of the invention. Accordingly, the above disclosure shouldbe construed as limited only by the metes and bounds of appended claims.

What is claimed is:
 1. A fluid injection head structure comprising: asubstrate; at least one bubble generator positioned on the substrate; atleast one functional device positioned on the substrate to control thebubble generator; a first conductive trace composed of a poly-siliconlayer; and a second conductive trace that electrically couples thefunctional device with the bubble generator, and couples the functionaldevice with the first conductive trace.
 2. The fluid injection headstructure of claim 1 further comprising a contact layer positionedbetween the first conductive trace and the second conductive trace toelectrically couple the first conductive trace with the secondconductive trace.
 3. The fluid injection head structure of claim 1wherein the second conductive trace comprises at least one pad.
 4. Thefluid injection head structure of claim 1 further comprising adielectric layer positioned between the first conductive trace and thesecond conductive trace.
 5. The fluid injection head structure of claim1 wherein the functional device is a transistor comprising a source, adrain, and a gate.
 6. The fluid injection head structure of claim 5wherein the transistor is a metal oxide semiconductor field effecttransistor (MOSFET) and the gate is composed of poly-silicon.
 7. Thefluid injection head structure of claim 6 wherein the gate and the firstconductive trace are formed in a same photo-etching process (PEP), 8.The fluid injection head structure of claim 1 wherein the material ofthe second conductive trace is any one of aluminum, gold, copper,tungsten, alloys of aluminum-silicon-copper, and alloys ofaluminum-copper.
 9. The fluid injection head structure of claim 1further comprising: at least one chamber positioned on the substrate,wherein each chamber comprises at least one orifice through to thesurface of the substrate; and at least one manifold connected to thechamber for allowing fluid to flow into the chamber.
 10. The injectionhead structure of claim 9 wherein the bubble generator comprises a firstbubble generating device and a second bubble generating devicepositioned adjacent to a corresponding orifice on a correspondingchamber, wherein when the chamber is full of fluid, the first bubblegenerating device generates a first bubble, and then the second bubblegenerating device generates a second bubble to eject the fluid from thechamber through the orifice.
 11. The injection head structure of claim10 wherein the first bubble serves as a virtual valve, restricts flow offluid out of the chamber.
 12. The injection head structure of claim 9wherein the injection head is used as a print head of an inkjet printer,the manifold is connected to an ink cartridge, and the fluid is the inkof the ink cartridge.
 13. A method for fabricating a fluid injectionhead structure comprising steps of: providing a substrate; forming atleast one bubble generator on the substrate; forming at least onefunctional device; forming a first conductive trace, which is composedof the poly-silicon layer; and forming a second conductive trace, whichis used to electrically couple the functional device with the bubblegenerator, and also serves to couple the functional device with thefirst conductive trace.
 14. The method of claim 13 wherein the methodfurther comprises forming a contact layer positioned between the firstconductive trace and the second conductive trace to electrically couplethe first conductive trace with the second conductive trace.
 15. Themethod of claim 13 wherein the second conductive trace comprises a pad.16. The method of claim 13 wherein the method further comprises a stepof forming a dielectric layer between the first conductive trace and thesecond conductive trace.
 17. The method of claim 13 wherein thefunctional device is a transistor comprising a source, a drain and agate.
 18. The method of claim 17 wherein the transistor is a metal oxidesemiconductor field effect transistor (MOSFET) and the gate is composedof a poly-silicon layer.
 19. The method of claim 13 wherein the gate andthe first conductive trace are formed in a same photo-etching process(PEP).
 20. The method of claim 13 wherein the material of the secondconductive trace is any one of aluminum, gold, copper, tungsten, alloysof aluminum-silicon-copper, and alloys of aluminum-copper.
 21. Themethod of claim 13 wherein the bubble generator comprises a first bubblegenerating device and a second bubble generating device positionedadjacent to a corresponding orifice on a corresponding chamber, whereinwhen the chamber is full of fluid, the first bubble generating devicegenerates a first bubble, and then the second bubble generating devicegenerates a second bubble to eject the fluid from the chamber throughthe orifice.
 22. The method of claim 21 wherein the first bubble servesas a virtual valve, restricts flow of fluid out of the chamber.
 23. Themethod of claim 13 wherein the method further comprises the steps of:forming a dielectric layer on the substrate; etching the substrate andthe dielectric layer to form a manifold and at least one chamberconnected to the manifold such that fluid can flow through the manifoldto the chamber; and forming at least one orifice positioned adjacent tothe corresponding bubble generator, which is connected to the chamberfor ejecting the fluid.
 24. The method of claim 23 wherein the methodfurther comprises a step of: forming a low stress layer, wherein thebubble generator is formed on the low stress layer.
 25. The method ofclaim 23 wherein the injection head is used as a print head of an inkjetprinter, the manifold is connected to an ink cartridge, and the fluid isthe ink of ink cartridge.